Transport et qualité des sédiments fluviaux : de la variabilité spatio-temporelle à la gestion

River sediment transport and quality: from space and time variability to management

UMR Sisyphe Université Pierre et Marie Curie, Paris VI, Case 123, Tour 26, 5e étage, 4 place Jussieu, 75252 Paris Cedex 05 - Tél. : 01 44 27 51 48, Fax : 01 44 27 51 25

Auteur de correspondance : meybeck@biogeodis.jussieu.fr

Abstract

Levels and specific fluxes of Total Suspended Solids (TSS) are one of the most variable descriptor of riverine systems. Space variations in France range from 10 to nearly 10 000 t.km^-2 y^-1 depending on rock type and slopes, Daily transport (kg km^-2.d^-1; mg/L) variability ranges over 2 to 40 orders of magnitude and decreases with higher stream order. The quantity of annual sediment load discharged in 1 % of time (duration pattern) varies from 9 to 81 %. In the Mediterranean river regime this duration pattern must also take into account rare flood events (> 20 y) that carry in one event the normal annual load. Anthropogenic influences are multiple (land use change, pollution, daming, dredging) and may affect sediment production, routing and retention as well as sediment composition. Metal chemistry of TSS is one of the best indicators of river system quality, although still not routinely monitored. The Seine River basin example provides a marked upstream - downstream gradient of contamination showing major discrepancies between least sensible elements (Co, Ba, As, ... ) and most sensitive elements (Cd, Hg, Zn). Sediment management in an impacted river basin involves land use, hydropower, fluvial transportation, urbanization, waste management, water quality and aquatic biodiversity management at various time scales ranging from few months to 100 years, which would include multiple stake holders and consider long-term issues.